1. Technical Field of the Invention
The present invention relates to a tool track display device which displays a track of a tool for a machine tool which machines a workpiece while reciprocally moving the tool and/or the workpiece relative to each other by at least one drive axle using a numerical control (NC) device.
2. Description of the Related Art
Conventionally, there are track display devices in which a track of a tool is indicated in different display attributes to examine the cause of a flaw which occurs in the actual track.
In Japanese Patent No. 3834268, the tool track is indicated by a set of minute line segments. The inclination of each minute line segment with respect to a specific axis is judged and the tool track consisting of a set of minute line segments is indicated using a display attribute which is determined in accordance with the judged inclination. In this case, the unevenness which occurs in the tool track can be easily determined.
In a machine tool in which machining is performed by controlling a plurality of servo shafts, there are cases where a workpiece is machined while a tool is reciprocally moved relative to the workpiece. In such a machining operation, when a commanded curve for the tool consists of a plurality of curves having different curvatures, the normal acceleration changes stepwise at the junctions between the curves. As a result, the influence of the acceleration change changes depending on the motion direction of the tool, so that the position where a track deviation between the commanded track and the actual track increases and the amount of the track deviation change.
Therefore, even if the profile of the commanded track is the same, the track deviation differs between the forward path and the return path. Nevertheless, in conventional track display devices, the commanded track and the actual track are displayed as they are without distinguishing the forward path and the return path. Consequently, it is impossible to correlate the track deviation with the motion direction, and accordingly, it is difficult to determine whether or not a track deviation has occurred based on the servo adjustment or on the motion direction.
Note that in Japanese Patent No. 3834268, the tool track is displayed based on NC data produced by the CAD, etc. Accordingly, it is impossible to display the NC-commanded track and the actual track of the movement of the tip point of the tool. Therefore, in Japanese Patent No. 3834268, it is impossible to confirm the track deviation between the commanded track and the actual track, and accordingly, an appropriate servo control cannot be performed to eliminate the track deviation.
Moreover, in Japanese Patent No. 3834268, the display attribute can be modified in accordance with the inclinations of the minute line segments, but it is impossible to modify the display attribute depending on the motion direction (forward motion or return motion). Therefore, whether the track deviation is caused due to the servo control or due to the motion direction cannot be correctly determined.
Under these circumstances, it is an object of the present invention to provide a tool track display device which is capable of correlating the track deviation and the motion direction so as to effectively perform servo control.